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MOND, a Paper and a Question
arXiv.org just posted a paper on MOND, here is the abstract:
================================================== ============ astro-ph/0403694 [abs, ps, pdf, other] : Title: Relativistic gravitation theory for the MOND paradigm Authors: Jacob D. Bekenstein Comments: ReVTeX and 3 eps figures; 33 pages; submitted to Physical Review D The modified newtonian dynamics (MOND) paradigm of Milgrom can boast of a number of successful predictions regarding galactic dynamics; these are made without the assumption that dark matter plays a significant role. MOND requires gravitation to depart from Newtonian theory in the extragalactic regime where dynamical accelerations are small. So far relativistic gravitation theories proposed to underpin MOND have either clashed with the post-Newtonian tests of general relativity, or failed to provide significant gravitational lensing, or violated hallowed principles by exhibiting superluminal scalar waves or an a priori vector field. We develop a relativistic MOND inspired theory which resolves these problems. In it gravitation is mediated by metric, a scalar field and a 4-vector field, all three dynamical. For a simple choice of its free function, the theory has a Newtonian limit for nonrelativistic dynamics with significant acceleration, but a MOND limit when accelerations are small. We calculate the beta and gamma PPN coefficients showing them to agree with solar system measurements. The gravitational light deflection by nonrelativistic systems is governed by the same potential responsible for dynamics of particles. Consequently, the new theory predicts gravitational lensing by extragalactic structures that cannot be distinguished from that predicted within the dark matter paradigm by general relativity. Cosmological models based on the theory are quite similar to those based on general relativity; they predict slow evolution of the scalar field. For a range of initial conditions, this last result makes it easy to rule out superluminal propagation of metric, scalar and vector waves. ================================================== =================== And a question. We now know of galaxies that do not exhibit the higher rotational velocities that are, presumably, diagnostic of Dark Matter. These galaxies also seem to have all gas stripped. This has been intepreted as implying that DM is a gas ( WIMPs rather that MACHOs ). Doesn't this contradict the predictions of MOND? The dynamics should be invarient and not depend on the enviromental history of the galaxy? Dark skies, tom -- We have discovered a therapy ( NOT a cure ) for the common cold. Play tuba for an hour. |
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